Method of dissolving steel to obtain residue containing aluminum nitride



1950 H. F. BEEGHLY METHOD OF DISSOLVING STEEL TO OBTAIN RESIDUE CONTAINING ALUMINUM NITRIDE Flled July 14, 1948 JNVENTOR. HUGH F.'BEEGH LY Patented Oct. 24, 1950 METHOD OF D ISSOLVING STEEL TO OB- TAIN RESIDUE CONTAINING ALUMI- NUM NITRIDE Hugh F. Beeghly, Whitehall, Pa.., assignor to Jones & Laughlin Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania,

Application July 14 1948, SerialflNo; 38,690

This invention relates to a method for extracting aluminum nitride from steel.

An object of m invention is to provide a method for extracting aluminum nitride from steel known to contain both nitrogen and aluminum. Another object is to provide such a method adapted for routine use. Another object is to provide means for distinguishing between the metallic aluminum, aluminum nitride and aluminum Oxide contents of steel known to contain aluminum, nitrogen and oxygen. Other objects will appear in the course of the description of my invention.

In the art of steelmaking it is common practice to add aluminum to the steel just before casting into ingots, or even in the ingot mold, for the purpose of deoxidizing the metal. This aluminum combines with the oxygen liberated during cooling of the steel to form solid deoxidation products, thus converting a gas to a solid and eliminating the blowholes which it might otherwise form. Steel so treated is called deoxidized or killed steel by steelmakers. Oxygen, however, is not the only element in' the molten steel which combines with aluminum. Nitrogen in steel also combines with aluminum to form aluminum nitride. Aluminum nitride in steel exerts a strong effect on many properties of steel, particularly its cold-working properties. It is therefore important to be able to accurately determine the amount of aluminum nitride in steel in order to better control the steelmaking and steel processing operations. Up until the present invention, however, no method for accurately determining the aluminumnitride content of steel was known. My invention provides such method.

In the past, the principal difliculty has been that the procedures commonly used to dissolve steel samples for conventional analysis caused aluminum nitride to dissociate. My invention consists in the discovery of a class of reagents which can be employed to dissolve a steel sample without dissolving or dissociating the aluminum nitride present, and in appropriate procedurefor the use of such reagents. My invention makes possible the separation from a steel sample of a solid residue containing the aluminum nitride originally present. The amount of aluminum nitride in this residue is then determined by analyzing for nitrogen by known means; The presence of other aluminum compounds in the residue, such as A1203, does not affect the analytical results.

The reagents which I have discovered to be 8 Claims. (01. 23-23% most suitable for my halogens in organic esters. for determining oxides in steel is, of course, well known but these procedures are not adapted to the determination of aluminum nitride. 'The ester-halogen reagents I have discovered have the valuable property of dissolving the steel rapidly without dissociating aluminum nitride. They are, however, more difiicult to use than the aqueous solutions of halogens or acids conventionall employed, as certain of them evaporate rapidly in open containers and on combination with water vapor form highly corrosive vapors.

For this reason it is impractical to use these reagents in open containers.

I have found that two types of apparatus in common use for other purposesmay be adapted to the practice of my invention. These are extractors and reflux units, both conventionlly used for separating soluble, non-volatile constituents from an insolublematrix by means of a volatile The procedure using each of these apj paratus' is described in detail in the following solvent.

paragraphs, the reagentrnentioned being a solution of bromine in methyl acetate. This reagent) is chosen for purposes of illustration only, as my invention comprises other mixtures of halogens and organic esters, which will appear.

A conventional Soxhlet extractor and asso ciated apparatus are shown in the drawing, to

. thimble. 14 having a porous bottom I5 is located;

in .the extraction chamber.

A suitable quantity of analytical grade anhy-f. drousester is placed in the distilling flask I, a. sample of steel is placed into a weighed extraction.

thi'mble I4, the thimble and contents are placed in purpose are solutions of The use of halogens The 1 A siphon tube, H- com municates at its end I2 with the ,mwe edd of extraction chamber'B and at its end I3 witl'iIthe, lower end 2 leading to the distilling flask." A

distilling flask by any convenient means at a rate sufficient to start and maintain a slow vaporization of the ester. The ester vapors rise from the distilling flask and pass through vapor tube I into the extraction chamber and up into the bottom of the condenser. Here the temperature i below the boiling point of the ester, causing the ester to condense and drip down into the extraction thimble containing the sample and bromine. Solution of the steel starts immediately.

The soluble reaction products of steel with bromine diffus through the porous bottom of the thimble along with the ester and the unreacted bromine and accumulate in the extraction chamber. Non-reacting constituents are retained in the thimble. When a volume of ester has condensed into the thimble sufficient to raise the liquid level in the extraction chamber above the top I! of the siphon tube the solution siphons down into the distilling flask. This flask then contains essentially a three-component solution: bromine, ester, and the reaction products. The vapor pressure of the reaction products compared to those of bromine and the ester is very low and they will, therefore, remain in the distilling flask, while the ester and bromine will be vaporized and the extraction cycle repeated. Extraction is continued until the extractant diffusing from the thimble becomes a deep amber color, (This is the characteristic color of ester-bromine solutions and is appreciabl lighter and of a different hue than that of solutions of equivalent concentration containing appreciable amounts of the reaction products.) At this stage of the extraction a strong magnet held to the side of the extraction chamber will attract any undecomposed particles of steel to the wall of the thimble. When such particles are detected, more bromine is added to the extractor and the extraction is continued until the sample is dissolved completely.

A second distilling flask containing only pure ester is then substituted for the one containing the original extractant and reaction products. The extraction is resumed and continued until the extractant diffusing from the thimble is water white. The heat is then shut off, the thimble removed and, with its contents, dried at a temperature slightly over 100 C. to a constant weight, cooled in a desiccator and weighed. In this manner the total weight of the residue is obtained. The residue is then removed from the thimble and its nitrogen content determined by conventional means. A convenient method is that described by H. F. Beeghly in the Analytical Edition of Industrial and Engineering Chemistry, vol. 14, p. 137, 1942.

The reflux unit which I also find suitable for the carrying out of my invention is similar to the extractor shown in Figure 1, except that the extractor 3 and thimble M are omitted and the condenser 4 with its cooling jacket 5 is connected directly to the distilling flask l. The sample is placed in the flask, the pure halogen added in the desired amount and the unit assembled. The desired amount of ester is then added through the top of th condenser. The sample dissolves directly in contact with all of the reaction products; the solvent refiuxes directly and continuously back into the flask. It is necessary with this method of procedure to separate the residue from the solvent solution by filtration or other suitable means and remove the excess solvent and reaction products from the residue by washing with successive portions of the pure ester, but in all other re 4 spects the method employing the reflux unit is identical with that making use of the extractor.

Having now described specifically the procedures effective in carrying out my invention and the apparatus I employ, I return to the reagents themselves, which previously have not been discussed in detail. The halogens comprise, of course, iodine, bromine, chlorine and fluorine. The latter two, being gases at room temperature, are difficult to employ. I prefer to use iodine or bromine, although I do not exclude the gaseous halogens from the scope of my invention. Bromine attacks the steel faster than does iodine, so fast, in fact, that the reaction may be explosive if not properly controlled. This is not the case with iodine. On the other hand, iodine requires an appreciably longer time to dissolve the steel than does bromine. The actual reaction between halogen and steel is believed to be:

2F'e 3X2 2FeXe (Iron) (Halogen) (Iron halide) Although it thus appears that the ester plays no part in the actual dissolution of the steel, it is essential to my invention, as it causes the above described reaction to take place in such a Way that the aluminum nitride is not decomposed, but remains in the residue as a solid. The ester also serves another essential purpose; it acts as a solvent for the reaction products of the halogen with the iron, which otherwise would remain in the residue as solids.

The esters which I find particularly suitable for my purpose are the aliphatic esters. By way of example, but not limitation, I find methyl, ethyl, propyl and butyl esters of acetic acid, and the corresponding esters of formic acid and propionic acid to operate successfully with iodine and bromine. No reason is known why esters of other normal saturated aliphatic acids could not be used. However, the greater the number of C atoms in the molecule, the greater the likelihood of decomposition and side reactions. The longer chain esters, when subjected to prolonged refluxing with halogens, show some tendency to crack or decompose, with the deposition of carbon, which, while not detrimental to the nitrogen analysis, may be objectionable when the residue is to be used for other studies. However, normal acetate esters containing less than five substituted carbon atoms show no noticeable tendency to deposit carbon even when heated in contact with halogens for intervals as long as 24 hours. Aromatic esters which can be used are methyl benzoate, ethyl benzoate and benzyl phthalate. These esters contain one or more aromatic molecules and while they can be used, their use is inadvisable because the ring structure reacts with the halogen and consumes the halogen. The quantity of halogen necessary is thereby increased greatly over that required to achieve the same effect with an aliphatic ester. The technique becomes more diflicult and the end result is less satisfactory because of the products of side reactions of the halogen with the ester.

It is desirable that the vapor pressure of the ester at temperatures below its boiling point approach as closely as possible to the vapor pressure of the halogen used. The closer this approach, the more amenable to control Will be the solution of the ester and halogen. In general, esters, particularly aliphatic esters, can be selected with curves of vapor pressure against temperatures that do not diverge too widely from those of the halogen being used, and the selection of an appropriate ester therfore is not diflicult. I have found, for example, that the vapor pressures of bromine and methyl acetate are nearly identical over a temperature range of 20 C. to 60 C.

The ratio of halogen to ester can be varied over a considerable range without affecting the nitrogen content of the residue. The proportions actually used may therefore be largely dictated by considerations of convenience or economy, as long as enough balogen to dissolve the steel is employed. For the bromine-methyl acetate solution mentioned in the previous paragraph I find convenient and effective proportions to be 2 ml. of bromine and 15 ml. of methyl acetate per gram of steel.

Although I have described certain preferred embodiments of my invention, I do not limit it thereto. It will be understood that the scope of my invention is limited only by the appended claims.

I claim:

1. A method of dissolving a steel sample Without disassociating the aluminum nitride originally present therein, which comprises reacting the steel sample with a solution of a halogen in an organic ester.

2. In a method of analyzing a steel sample for its aluminum nitride content, the steps of dissolving the sample in a solution of a halogen in an organic ester and separating the aluminum nitride-containing residue from the solution.

3. In a method of analyzing a steel sample for its aluminum nitride content, the steps of dissolving the sample in a solution of a halogen in an aliphatic ester and separating the aluminum nitride-containing residue from the solution.

4. In a method of analyzing a steel sample for its aluminum nitride content, the steps of dissolving the sample in a solution of a normally non-gaseous halogen in an aliphatic ester and separating the aluminum nitride-containing residue from the solution.

5. In a method of analyzing a steel sample for its aluminum nitride content, the steps of dissolving the sample in a solution of a normally non-gaseous halogen in an aliphatic ester, said ester having vapor pressure-temperature characteristics similar to those of the halogen, and separating the aluminum nitride-containing residue from the solution.

6. In a method of analyzing a steel sample for its aluminum nitride content, the steps of dissolving the sample in a solution of bromine in methyl acetate and separating the aluminum.

nitride-containing residue from the solution.

7. A method of determining the aluminum nitride content of a steel sample, comprising the non-gaseous halogen in an ester selected from the group consisting of the methyl, ethyl, propyl and butyl esters of acid selected from the group consisting of acetic acid, formic acid and propionic acid, and separating the aluminum nitride-containing residue from the solution.

HUGH F. BEEGHLY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Number Hayes et a1 Feb. 16, 1937 

7. A METHOD OF DETERMINING THE ALUMINUM NITRIDE CONTENT OF A STEEL SAMPLE, COMPRISING THE STEPS OF DISSOLVING THE STEEL IN A SOLUTION OF A HALOGEN IN AN ORGANIC ESTER, SEPARATING THE ALUMINUM NITRIDE-CONTAINING RESIDUE FROM THE SOLUTION, AND TREATING THE SAID RESIDUE TO DETERMINE ITS NITROGEN CONTENT, FROM WHICH THE AMOUNT OF ALUMINUM NITRIDE IN THE RESIDUE MAY READILY BE CALCULATED TO DETERMINE THE AMOUNT OF ALUMINUM NITRIDE IN THE STEEL. 